Clothing has been produced from fabrics obtained by blending hygroscopic, heat-generating fibers, such as cellulose fibers for use as clothing that undergoes a rise in temperature when worn, and clothing is known that causes heat to be generated by insensible water loss and perspiration from the body when worn (see, for example, Patent Document 1). However, once the amount of moisture absorbed by hygroscopic, heat-generating fibers reaches saturated level, there is no further generation of heat, which not only resulted in a short duration of heat generation, but also even caused the wearer to feel cold due to moisture present in the fibers. Moreover, although clothing incorporating a heater, such as a planar heating element or a linear heating element is also known for use as an exothermic fabric or exothermic cloth other than that employing hygroscopic heat generation, since all of these generate heat by electricity, they are heavy when worn as clothing and require electrodes, thereby making movement difficult.
In addition, a knitted fabric has recently been proposed that has a heat generation function, i.e., completely different from that employed in the past in which heat is generated during stretching of the knitted fabric during a body movement when worn (see, for example, Patent Document 2 and Patent Document 3).